It is particularly useful to be able to adapt the pitch of the blades of the fan of an engine to different flight conditions so as to obtain optimum engine performance and thrust reversal. The energy output of the engine can be optimized by varying the blade pitch to suit specific operating conditions.
Devices for controlling the variation of blade pitch usually comprise hydraulic actuators which drive gears to move the blades into the required position. These devices are complex, bulky and unreliable.
Alternatively, there are electric drive systems for controlling the pitch of rotor blades. These systems usually use direct current (dc) motors activated and deactivated by relays powered from the aircraft dc bus, and comprise means for transmitting electric power using electrical contacts between a commutator and brushes. These contacts are subject to wear, causing reliability problems.
Accordingly, it is an object of the invention to obviate the disadvantages of the known devices and to provide a control device for varying the pitch of rotor blades which is simple, reliable, light and compact.